Motor Control

[Subscuba@aol.com]

Steve, 

In response to your questions about motor controls. This seems to be a
weakness with most people. The current engineering interests lie primarily
with digital electronics and not the power switching field. Don't use a light
dimmer with a DC motor.

I designed my own motor controller due to being able to do so at little cost
out of my pocket. The parts cost about $80 and handles 60 amperes from 36
volts, your application is higher power. The design does not use an "H" or
full bridge since the efficiency of the "H" bridge is lower than a single
ended approach (single ended means only one power switch is used instead of
four, also the batteries last longer). This makes reversing more difficult but
I used a reversing relay since most of the time I'm going forward, I hope. If
you are not familar with high current switching and electronic construction
you would probably be better off buying ($$$) an existing motor controller
using a full bridge as suggested by Dave Everett. Take a look at the Website
Dave suggested. If you want to go the hard way and do it yourself I'll be glad
to help, I have a background and interest in this area. The higher currents
involved ask for multiple FETs (Field Effect Transistors) but cost almost
dictates IGBTs (Insulated Gate Bipolar Transistors). Both devices switch very
fast but the IGBT is slower at turn off and has a higher ON voltage, in
general.

One problem in using the technique Gary is using is that it is difficult to
use all the batteries capacity so you may not be using all the batteries you
take along. With modern  power switching circuits you essentially use all the
batteries you have with potential advantages of longer battery life and lower
depth of discharge. 

I wish you luck on using the air cooled motor you have. I would be concerned
about the air flow around and through the motor. Bear in mind the motor
controller will also have to be cooled.

Ken Martindale